<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>回顾一个DOM操作</title>
  <style>
    .demo {
      background-color: orange;
    }
  </style>
</head>
<body>
  <button id="btn">点我创建一个输入框</button>

  <script>
    const btn = document.getElementById('btn')
    btn.onclick = () => {
      const input = document.createElement('input')

      input.className = 'demo'
      input.value = 99
      input.onclick = () => {alert(1)}

      document.body.appendChild(input)

      input.focus()
      input.parentElement.style.backgroundColor = 'skyblue'
    }
  </script>
</body>
</html>